digitalbitbox.py

# ----------------------------------------------------------------------------------
# Electrum plugin for the Digital Bitbox hardware wallet by Shift Devices AG
# digitalbitbox.com
#

try:
    from electrum.crypto import Hash, EncodeAES, DecodeAES
    from electrum.bitcoin import (TYPE_ADDRESS, push_script, var_int, public_key_to_p2pkh, is_address,
                                  serialize_xpub, deserialize_xpub)
    from electrum import ecc
    from electrum.ecc import msg_magic
    from electrum.wallet import Standard_Wallet
    from electrum import constants
    from electrum.transaction import Transaction
    from electrum.i18n import _
    from electrum.keystore import Hardware_KeyStore
    from ..hw_wallet import HW_PluginBase
    from electrum.util import print_error, to_string, UserCancelled
    from electrum.base_wizard import ScriptTypeNotSupported, HWD_SETUP_NEW_WALLET

    import time
    import hid
    import json
    import math
    import binascii
    import struct
    import hashlib
    import requests
    import base64
    import os
    import sys
    DIGIBOX = True
except ImportError as e:
    DIGIBOX = False



# ----------------------------------------------------------------------------------
# USB HID interface
#

def to_hexstr(s):
    return binascii.hexlify(s).decode('ascii')

class DigitalBitbox_Client():

    def __init__(self, plugin, hidDevice):
        self.plugin = plugin
        self.dbb_hid = hidDevice
        self.opened = True
        self.password = None
        self.isInitialized = False
        self.setupRunning = False
        self.usbReportSize = 64 # firmware > v2.0.0


    def close(self):
        if self.opened:
            try:
                self.dbb_hid.close()
            except:
                pass
        self.opened = False


    def timeout(self, cutoff):
        pass


    def label(self):
        return " "


    def is_pairable(self):
        return True


    def is_initialized(self):
        return self.dbb_has_password()


    def is_paired(self):
        return self.password is not None

    def has_usable_connection_with_device(self):
        try:
            self.dbb_has_password()
        except BaseException:
            return False
        return True

    def _get_xpub(self, bip32_path):
        if self.check_device_dialog():
            return self.hid_send_encrypt(('{"xpub": "%s"}' % bip32_path).encode('utf8'))


    def get_xpub(self, bip32_path, xtype):
        assert xtype in self.plugin.SUPPORTED_XTYPES
        reply = self._get_xpub(bip32_path)
        if reply:
            xpub = reply['xpub']
            # Change type of xpub to the requested type. The firmware
            # only ever returns the mainnet standard type, but it is agnostic
            # to the type when signing.
            if xtype != 'standard' or constants.net.TESTNET:
                _, depth, fingerprint, child_number, c, cK = deserialize_xpub(xpub, net=constants.BitcoinMainnet)
                xpub = serialize_xpub(xtype, c, cK, depth, fingerprint, child_number)
            return xpub
        else:
            raise Exception('no reply')


    def dbb_has_password(self):
        reply = self.hid_send_plain(b'{"ping":""}')
        if 'ping' not in reply:
            raise Exception(_('Device communication error. Please unplug and replug your Digital Bitbox.'))
        if reply['ping'] == 'password':
            return True
        return False


    def stretch_key(self, key):
        import hmac
        return to_hexstr(hashlib.pbkdf2_hmac('sha512', key.encode('utf-8'), b'Digital Bitbox', iterations = 20480))


    def backup_password_dialog(self):
        msg = _("Enter the password used when the backup was created:")
        while True:
            password = self.handler.get_passphrase(msg, False)
            if password is None:
                return None
            if len(password) < 4:
                msg = _("Password must have at least 4 characters.") \
                      + "\n\n" + _("Enter password:")
            elif len(password) > 64:
                msg = _("Password must have less than 64 characters.") \
                      + "\n\n" + _("Enter password:")
            else:
                return password.encode('utf8')


    def password_dialog(self, msg):
        while True:
            password = self.handler.get_passphrase(msg, False)
            if password is None:
                return False
            if len(password) < 4:
                msg = _("Password must have at least 4 characters.") + \
                      "\n\n" + _("Enter password:")
            elif len(password) > 64:
                msg = _("Password must have less than 64 characters.") + \
                      "\n\n" + _("Enter password:")
            else:
                self.password = password.encode('utf8')
                return True


    def check_device_dialog(self):
        # Set password if fresh device
        if self.password is None and not self.dbb_has_password():
            if not self.setupRunning:
                return False # A fresh device cannot connect to an existing wallet
            msg = _("An uninitialized Digital Bitbox is detected.") + " " + \
                  _("Enter a new password below.") + "\n\n" + \
                  _("REMEMBER THE PASSWORD!") + "\n\n" + \
                  _("You cannot access your coins or a backup without the password.") + "\n" + \
                  _("A backup is saved automatically when generating a new wallet.")
            if self.password_dialog(msg):
                reply = self.hid_send_plain(b'{"password":"' + self.password + b'"}')
            else:
                return False

        # Get password from user if not yet set
        msg = _("Enter your Digital Bitbox password:")
        while self.password is None:
            if not self.password_dialog(msg):
                raise UserCancelled()
            reply = self.hid_send_encrypt(b'{"led":"blink"}')
            if 'error' in reply:
                self.password = None
                if reply['error']['code'] == 109:
                    msg = _("Incorrect password entered.") + "\n\n" + \
                          reply['error']['message'] + "\n\n" + \
                          _("Enter your Digital Bitbox password:")
                else:
                    # Should never occur
                    msg = _("Unexpected error occurred.") + "\n\n" + \
                          reply['error']['message'] + "\n\n" + \
                          _("Enter your Digital Bitbox password:")

        # Initialize device if not yet initialized
        if not self.setupRunning:
            self.isInitialized = True # Wallet exists. Electrum code later checks if the device matches the wallet
        elif not self.isInitialized:
            reply = self.hid_send_encrypt(b'{"device":"info"}')
            if reply['device']['id'] != "":
                self.recover_or_erase_dialog() # Already seeded
            else:
                self.seed_device_dialog() # Seed if not initialized
            self.mobile_pairing_dialog()
        return self.isInitialized


    def recover_or_erase_dialog(self):
        msg = _("The Digital Bitbox is already seeded. Choose an option:") + "\n"
        choices = [
            (_("Create a wallet using the current seed")),
            (_("Load a wallet from the micro SD card (the current seed is overwritten)")),
            (_("Erase the Digital Bitbox"))
        ]
        try:
            reply = self.handler.win.query_choice(msg, choices)
        except Exception:
            return # Back button pushed
        if reply == 2:
            self.dbb_erase()
        elif reply == 1:
            if not self.dbb_load_backup():
                return
        else:
            if self.hid_send_encrypt(b'{"device":"info"}')['device']['lock']:
                raise Exception(_("Full 2FA enabled. This is not supported yet."))
            # Use existing seed
        self.isInitialized = True


    def seed_device_dialog(self):
        msg = _("Choose how to initialize your Digital Bitbox:") + "\n"
        choices = [
            (_("Generate a new random wallet")),
            (_("Load a wallet from the micro SD card"))
        ]
        try:
            reply = self.handler.win.query_choice(msg, choices)
        except Exception:
            return # Back button pushed
        if reply == 0:
            self.dbb_generate_wallet()
        else:
            if not self.dbb_load_backup(show_msg=False):
                return
        self.isInitialized = True

    def mobile_pairing_dialog(self):
        dbb_user_dir = None
        if sys.platform == 'darwin':
            dbb_user_dir = os.path.join(os.environ.get("HOME", ""), "Library", "Application Support", "DBB")
        elif sys.platform == 'win32':
            dbb_user_dir = os.path.join(os.environ["APPDATA"], "DBB")
        else:
            dbb_user_dir = os.path.join(os.environ["HOME"], ".dbb")

        if not dbb_user_dir:
            return

        try:
            # Python 3.5+
            jsonDecodeError = json.JSONDecodeError
        except AttributeError:
            jsonDecodeError = ValueError
        try:
            with open(os.path.join(dbb_user_dir, "config.dat")) as f:
                dbb_config = json.load(f)
        except (FileNotFoundError, jsonDecodeError):
            return

        if 'encryptionprivkey' not in dbb_config or 'comserverchannelid' not in dbb_config:
            return

        choices = [
            _('Do not pair'),
            _('Import pairing from the Digital Bitbox desktop app'),
        ]
        try:
            reply = self.handler.win.query_choice(_('Mobile pairing options'), choices)
        except Exception:
            return # Back button pushed

        if reply == 0:
            if self.plugin.is_mobile_paired():
                del self.plugin.digitalbitbox_config['encryptionprivkey']
                del self.plugin.digitalbitbox_config['comserverchannelid']
        elif reply == 1:
            # import pairing from dbb app
            self.plugin.digitalbitbox_config['encryptionprivkey'] = dbb_config['encryptionprivkey']
            self.plugin.digitalbitbox_config['comserverchannelid'] = dbb_config['comserverchannelid']
        self.plugin.config.set_key('digitalbitbox', self.plugin.digitalbitbox_config)

    def dbb_generate_wallet(self):
        key = self.stretch_key(self.password)
        filename = ("Electrum-" + time.strftime("%Y-%m-%d-%H-%M-%S") + ".pdf")
        msg = ('{"seed":{"source": "create", "key": "%s", "filename": "%s", "entropy": "%s"}}' % (key, filename, 'Digital Bitbox Electrum Plugin')).encode('utf8')
        reply = self.hid_send_encrypt(msg)
        if 'error' in reply:
            raise Exception(reply['error']['message'])


    def dbb_erase(self):
        self.handler.show_message(_("Are you sure you want to erase the Digital Bitbox?") + "\n\n" +
                                  _("To continue, touch the Digital Bitbox's light for 3 seconds.") + "\n\n" +
                                  _("To cancel, briefly touch the light or wait for the timeout."))
        hid_reply = self.hid_send_encrypt(b'{"reset":"__ERASE__"}')
        self.handler.finished()
        if 'error' in hid_reply:
            raise Exception(hid_reply['error']['message'])
        else:
            self.password = None
            raise Exception('Device erased')


    def dbb_load_backup(self, show_msg=True):
        backups = self.hid_send_encrypt(b'{"backup":"list"}')
        if 'error' in backups:
            raise Exception(backups['error']['message'])
        try:
            f = self.handler.win.query_choice(_("Choose a backup file:"), backups['backup'])
        except Exception:
            return False # Back button pushed
        key = self.backup_password_dialog()
        if key is None:
            raise Exception('Canceled by user')
        key = self.stretch_key(key)
        if show_msg:
            self.handler.show_message(_("Loading backup...") + "\n\n" +
                                      _("To continue, touch the Digital Bitbox's light for 3 seconds.") + "\n\n" +
                                      _("To cancel, briefly touch the light or wait for the timeout."))
        msg = ('{"seed":{"source": "backup", "key": "%s", "filename": "%s"}}' % (key, backups['backup'][f])).encode('utf8')
        hid_reply = self.hid_send_encrypt(msg)
        self.handler.finished()
        if 'error' in hid_reply:
            raise Exception(hid_reply['error']['message'])
        return True


    def hid_send_frame(self, data):
        HWW_CID = 0xFF000000
        HWW_CMD = 0x80 + 0x40 + 0x01
        data_len = len(data)
        seq = 0;
        idx = 0;
        write = []
        while idx < data_len:
            if idx == 0:
                # INIT frame
                write = data[idx : idx + min(data_len, self.usbReportSize - 7)]
                self.dbb_hid.write(b'\0' + struct.pack(">IBH", HWW_CID, HWW_CMD, data_len & 0xFFFF) + write + b'\xEE' * (self.usbReportSize - 7 - len(write)))
            else:
                # CONT frame
                write = data[idx : idx + min(data_len, self.usbReportSize - 5)]
                self.dbb_hid.write(b'\0' + struct.pack(">IB", HWW_CID, seq) + write + b'\xEE' * (self.usbReportSize - 5 - len(write)))
                seq += 1
            idx += len(write)


    def hid_read_frame(self):
        # INIT response
        read = bytearray(self.dbb_hid.read(self.usbReportSize))
        cid = ((read[0] * 256 + read[1]) * 256 + read[2]) * 256 + read[3]
        cmd = read[4]
        data_len = read[5] * 256 + read[6]
        data = read[7:]
        idx = len(read) - 7;
        while idx < data_len:
            # CONT response
            read = bytearray(self.dbb_hid.read(self.usbReportSize))
            data += read[5:]
            idx += len(read) - 5
        return data


    def hid_send_plain(self, msg):
        reply = ""
        try:
            serial_number = self.dbb_hid.get_serial_number_string()
            if "v2.0." in serial_number or "v1." in serial_number:
                hidBufSize = 4096
                self.dbb_hid.write('\0' + msg + '\0' * (hidBufSize - len(msg)))
                r = bytearray()
                while len(r) < hidBufSize:
                    r += bytearray(self.dbb_hid.read(hidBufSize))
            else:
                self.hid_send_frame(msg)
                r = self.hid_read_frame()
            r = r.rstrip(b' \t\r\n\0')
            r = r.replace(b"\0", b'')
            r = to_string(r, 'utf8')
            reply = json.loads(r)
        except Exception as e:
            print_error('Exception caught ' + str(e))
        return reply


    def hid_send_encrypt(self, msg):
        reply = ""
        try:
            secret = Hash(self.password)
            msg = EncodeAES(secret, msg)
            reply = self.hid_send_plain(msg)
            if 'ciphertext' in reply:
                reply = DecodeAES(secret, ''.join(reply["ciphertext"]))
                reply = to_string(reply, 'utf8')
                reply = json.loads(reply)
            if 'error' in reply:
                self.password = None
        except Exception as e:
            print_error('Exception caught ' + str(e))
        return reply



# ----------------------------------------------------------------------------------
#
#

class DigitalBitbox_KeyStore(Hardware_KeyStore):
    hw_type = 'digitalbitbox'
    device = 'DigitalBitbox'


    def __init__(self, d):
        Hardware_KeyStore.__init__(self, d)
        self.force_watching_only = False
        self.maxInputs = 14 # maximum inputs per single sign command


    def get_derivation(self):
        return str(self.derivation)


    def is_p2pkh(self):
        return self.derivation.startswith("m/44'/")


    def give_error(self, message, clear_client = False):
        if clear_client:
            self.client = None
        raise Exception(message)


    def decrypt_message(self, pubkey, message, password):
        raise RuntimeError(_('Encryption and decryption are currently not supported for {}').format(self.device))


    def sign_message(self, sequence, message, password):
        sig = None
        try:
            message = message.encode('utf8')
            inputPath = self.get_derivation() + "/%d/%d" % sequence
            msg_hash = Hash(msg_magic(message))
            inputHash = to_hexstr(msg_hash)
            hasharray = []
            hasharray.append({'hash': inputHash, 'keypath': inputPath})
            hasharray = json.dumps(hasharray)

            msg = ('{"sign":{"meta":"sign message", "data":%s}}' % hasharray).encode('utf8')

            dbb_client = self.plugin.get_client(self)

            if not dbb_client.is_paired():
                raise Exception(_("Could not sign message."))

            reply = dbb_client.hid_send_encrypt(msg)
            self.handler.show_message(_("Signing message ...") + "\n\n" +
                                      _("To continue, touch the Digital Bitbox's blinking light for 3 seconds.") + "\n\n" +
                                      _("To cancel, briefly touch the blinking light or wait for the timeout."))
            reply = dbb_client.hid_send_encrypt(msg) # Send twice, first returns an echo for smart verification (not implemented)
            self.handler.finished()

            if 'error' in reply:
                raise Exception(reply['error']['message'])

            if 'sign' not in reply:
                raise Exception(_("Could not sign message."))

            if 'recid' in reply['sign'][0]:
                # firmware > v2.1.1
                sig_string = binascii.unhexlify(reply['sign'][0]['sig'])
                recid = int(reply['sign'][0]['recid'], 16)
                sig = ecc.construct_sig65(sig_string, recid, True)
                pubkey, compressed = ecc.ECPubkey.from_signature65(sig, msg_hash)
                addr = public_key_to_p2pkh(pubkey.get_public_key_bytes(compressed=compressed))
                if ecc.verify_message_with_address(addr, sig, message) is False:
                    raise Exception(_("Could not sign message"))
            elif 'pubkey' in reply['sign'][0]:
                # firmware <= v2.1.1
                for recid in range(4):
                    sig_string = binascii.unhexlify(reply['sign'][0]['sig'])
                    sig = ecc.construct_sig65(sig_string, recid, True)
                    try:
                        addr = public_key_to_p2pkh(binascii.unhexlify(reply['sign'][0]['pubkey']))
                        if ecc.verify_message_with_address(addr, sig, message):
                            break
                    except Exception:
                        continue
                else:
                    raise Exception(_("Could not sign message"))


        except BaseException as e:
            self.give_error(e)
        return sig


    def sign_transaction(self, tx, password):
        if tx.is_complete():
            return

        try:
            p2pkhTransaction = True
            derivations = self.get_tx_derivations(tx)
            inputhasharray = []
            hasharray = []
            pubkeyarray = []

            # Build hasharray from inputs
            for i, txin in enumerate(tx.inputs()):
                if txin['type'] == 'coinbase':
                    self.give_error("Coinbase not supported") # should never happen

                if txin['type'] != 'p2pkh':
                    p2pkhTransaction = False

                for x_pubkey in txin['x_pubkeys']:
                    if x_pubkey in derivations:
                        index = derivations.get(x_pubkey)
                        inputPath = "%s/%d/%d" % (self.get_derivation(), index[0], index[1])
                        inputHash = Hash(binascii.unhexlify(tx.serialize_preimage(i)))
                        hasharray_i = {'hash': to_hexstr(inputHash), 'keypath': inputPath}
                        hasharray.append(hasharray_i)
                        inputhasharray.append(inputHash)
                        break
                else:
                    self.give_error("No matching x_key for sign_transaction") # should never happen

            # Build pubkeyarray from outputs
            for _type, address, amount in tx.outputs():
                assert _type == TYPE_ADDRESS
                info = tx.output_info.get(address)
                if info is not None:
                    index, xpubs, m = info
                    changePath = self.get_derivation() + "/%d/%d" % index
                    changePubkey = self.derive_pubkey(index[0], index[1])
                    pubkeyarray_i = {'pubkey': changePubkey, 'keypath': changePath}
                    pubkeyarray.append(pubkeyarray_i)

            # Special serialization of the unsigned transaction for
            # the mobile verification app.
            # At the moment, verification only works for p2pkh transactions.
            if p2pkhTransaction:
                class CustomTXSerialization(Transaction):
                    @classmethod
                    def input_script(self, txin, estimate_size=False):
                        if txin['type'] == 'p2pkh':
                            return Transaction.get_preimage_script(txin)
                        if txin['type'] == 'p2sh':
                            # Multisig verification has partial support, but is disabled. This is the
                            # expected serialization though, so we leave it here until we activate it.
                            return '00' + push_script(Transaction.get_preimage_script(txin))
                        raise Exception("unsupported type %s" % txin['type'])
                tx_dbb_serialized = CustomTXSerialization(tx.serialize()).serialize_to_network()
            else:
                # We only need this for the signing echo / verification.
                tx_dbb_serialized = None

            # Build sign command
            dbb_signatures = []
            steps = math.ceil(1.0 * len(hasharray) / self.maxInputs)
            for step in range(int(steps)):
                hashes = hasharray[step * self.maxInputs : (step + 1) * self.maxInputs]

                msg = {
                    "sign": {
                        "data": hashes,
                        "checkpub": pubkeyarray,
                    },
                }
                if tx_dbb_serialized is not None:
                    msg["sign"]["meta"] = to_hexstr(Hash(tx_dbb_serialized))
                msg = json.dumps(msg).encode('ascii')
                dbb_client = self.plugin.get_client(self)

                if not dbb_client.is_paired():
                    raise Exception("Could not sign transaction.")

                reply = dbb_client.hid_send_encrypt(msg)
                if 'error' in reply:
                    raise Exception(reply['error']['message'])

                if 'echo' not in reply:
                    raise Exception("Could not sign transaction.")

                if self.plugin.is_mobile_paired() and tx_dbb_serialized is not None:
                    reply['tx'] = tx_dbb_serialized
                    self.plugin.comserver_post_notification(reply)

                if steps > 1:
                    self.handler.show_message(_("Signing large transaction. Please be patient ...") + "\n\n" +
                                              _("To continue, touch the Digital Bitbox's blinking light for 3 seconds.") + " " +
                                              _("(Touch {} of {})").format((step + 1), steps) + "\n\n" +
                                              _("To cancel, briefly touch the blinking light or wait for the timeout.") + "\n\n")
                else:
                    self.handler.show_message(_("Signing transaction...") + "\n\n" +
                                              _("To continue, touch the Digital Bitbox's blinking light for 3 seconds.") + "\n\n" +
                                              _("To cancel, briefly touch the blinking light or wait for the timeout."))

                # Send twice, first returns an echo for smart verification
                reply = dbb_client.hid_send_encrypt(msg)
                self.handler.finished()

                if 'error' in reply:
                    if reply["error"].get('code') in (600, 601):
                        # aborted via LED short touch or timeout
                        raise UserCancelled()
                    raise Exception(reply['error']['message'])

                if 'sign' not in reply:
                    raise Exception("Could not sign transaction.")

                dbb_signatures.extend(reply['sign'])

            # Fill signatures
            if len(dbb_signatures) != len(tx.inputs()):
                raise Exception("Incorrect number of transactions signed.") # Should never occur
            for i, txin in enumerate(tx.inputs()):
                num = txin['num_sig']
                for pubkey in txin['pubkeys']:
                    signatures = list(filter(None, txin['signatures']))
                    if len(signatures) == num:
                        break # txin is complete
                    ii = txin['pubkeys'].index(pubkey)
                    signed = dbb_signatures[i]
                    if 'recid' in signed:
                        # firmware > v2.1.1
                        recid = int(signed['recid'], 16)
                        s = binascii.unhexlify(signed['sig'])
                        h = inputhasharray[i]
                        pk = ecc.ECPubkey.from_sig_string(s, recid, h)
                        pk = pk.get_public_key_hex(compressed=True)
                    elif 'pubkey' in signed:
                        # firmware <= v2.1.1
                        pk = signed['pubkey']
                    if pk != pubkey:
                        continue
                    sig_r = int(signed['sig'][:64], 16)
                    sig_s = int(signed['sig'][64:], 16)
                    sig = ecc.der_sig_from_r_and_s(sig_r, sig_s)
                    sig = to_hexstr(sig) + '01'
                    tx.add_signature_to_txin(i, ii, sig)
        except UserCancelled:
            raise
        except BaseException as e:
            self.give_error(e, True)
        else:
            print_error("Transaction is_complete", tx.is_complete())
            tx.raw = tx.serialize()


class DigitalBitboxPlugin(HW_PluginBase):

    libraries_available = DIGIBOX
    keystore_class = DigitalBitbox_KeyStore
    client = None
    DEVICE_IDS = [
                   (0x03eb, 0x2402) # Digital Bitbox
                 ]
    SUPPORTED_XTYPES = ('standard', 'p2wpkh-p2sh', 'p2wpkh', 'p2wsh-p2sh', 'p2wsh')

    def __init__(self, parent, config, name):
        HW_PluginBase.__init__(self, parent, config, name)
        if self.libraries_available:
            self.device_manager().register_devices(self.DEVICE_IDS)

        self.digitalbitbox_config = self.config.get('digitalbitbox', {})


    def get_dbb_device(self, device):
        dev = hid.device()
        dev.open_path(device.path)
        return dev


    def create_client(self, device, handler):
        if device.interface_number == 0 or device.usage_page == 0xffff:
            if handler:
                self.handler = handler
            client = self.get_dbb_device(device)
            if client is not None:
                client = DigitalBitbox_Client(self, client)
            return client
        else:
            return None


    def setup_device(self, device_info, wizard, purpose):
        devmgr = self.device_manager()
        device_id = device_info.device.id_
        client = devmgr.client_by_id(device_id)
        if client is None:
            raise Exception(_('Failed to create a client for this device.') + '\n' +
                            _('Make sure it is in the correct state.'))
        client.handler = self.create_handler(wizard)
        if purpose == HWD_SETUP_NEW_WALLET:
            client.setupRunning = True
        client.get_xpub("m/44'/0'", 'standard')


    def is_mobile_paired(self):
        return 'encryptionprivkey' in self.digitalbitbox_config


    def comserver_post_notification(self, payload):
        assert self.is_mobile_paired(), "unexpected mobile pairing error"
        url = 'https://digitalbitbox.com/smartverification/index.php'
        key_s = base64.b64decode(self.digitalbitbox_config['encryptionprivkey'])
        args = 'c=data&s=0&dt=0&uuid=%s&pl=%s' % (
            self.digitalbitbox_config['comserverchannelid'],
            EncodeAES(key_s, json.dumps(payload).encode('ascii')).decode('ascii'),
        )
        try:
            requests.post(url, args)
        except Exception as e:
            self.handler.show_error(str(e))


    def get_xpub(self, device_id, derivation, xtype, wizard):
        if xtype not in self.SUPPORTED_XTYPES:
            raise ScriptTypeNotSupported(_('This type of script is not supported with {}.').format(self.device))
        devmgr = self.device_manager()
        client = devmgr.client_by_id(device_id)
        client.handler = self.create_handler(wizard)
        client.check_device_dialog()
        xpub = client.get_xpub(derivation, xtype)
        return xpub


    def get_client(self, keystore, force_pair=True):
        devmgr = self.device_manager()
        handler = keystore.handler
        with devmgr.hid_lock:
            client = devmgr.client_for_keystore(self, handler, keystore, force_pair)
        if client is not None:
            client.check_device_dialog()
        return client

    def show_address(self, wallet, address, keystore=None):
        if keystore is None:
            keystore = wallet.get_keystore()
        if not self.show_address_helper(wallet, address, keystore):
            return
        if type(wallet) is not Standard_Wallet:
            keystore.handler.show_error(_('This function is only available for standard wallets when using {}.').format(self.device))
            return
        if not self.is_mobile_paired():
            keystore.handler.show_error(_('This function is only available after pairing your {} with a mobile device.').format(self.device))
            return
        if not keystore.is_p2pkh():
            keystore.handler.show_error(_('This function is only available for p2pkh keystores when using {}.').format(self.device))
            return
        change, index = wallet.get_address_index(address)
        keypath = '%s/%d/%d' % (keystore.derivation, change, index)
        xpub = self.get_client(keystore)._get_xpub(keypath)
        verify_request_payload = {
            "type": 'p2pkh',
            "echo": xpub['echo'],
        }
        self.comserver_post_notification(verify_request_payload)